Wearable device battery could last 10 years

Researchers have designed a battery that could keep wearable and health care devices running for 10 or more years without a recharge.

The new design, based on the lithium carbon fluoride (CFx) chemical formula, could also lead to batteries that are safer than current ones. A prototype battery based on the formula was tested by researchers at the U.S. Department of Energy's Oak Ridge National Laboratory, and a related paper was published in the Journal of the American Chemical Society last week.

The CFx batteries could be as small as coins, and could last for years in low-power fitness trackers or wearable devices with sensors, said researcher Chengdu Liang, the lead author of the paper.

"The battery is not going to be recharged. It's one-time use," Liang said.

Wearable devices typically transmit small bursts of information and don't demand much energy, which can prolong life of the CFx battery. The battery could be desirable for sensors and human implants like pacemakers, which are difficult to recharge or replace, Liang said.

The prototype CFx battery in its current form is not intended for use in computers and mobile devices, which consume more energy than sensors and rely on recharges, Liang said.

"This study is proof-of-concept research, but we have been contacted by a private company interested in commercializing the battery. It could become a reality in a few years depending on the commercialization timeline," Liang said.

Today's batteries do not last very long and some are considered unsafe. PC makers Sony and Lenovo recently reported cases of lithium-ion batteries causing laptops to overheat and burn.

Research for new batteries using zinc-air and lithium-air technology is underway. Some alternative batteries such as those using silver-zinc are considered too expensive. The promise of fuel cells is catching on with car makers.

To be sure, the CFx chemical formula for batteries isn't new. Special batteries based on the formula are apparently sold by companies like Contour Energy for use by the military in drones, night-vision goggles and other electronics. Those batteries are available in different sizes. Contour Energy did not respond to calls, and emails bounced back.

But according to existing research from the U.S. Army, the CFx chemical formula is "known to have one of the highest theoretical energy capacities compared to other popular lithium cell chemistries."

"It is based on the old theory and with the new design," ORNL's Liang said. "This is a big breakthrough."

During an experiment, the ORNL researchers developed and tested an actual CFx battery, but used a solid electrolyte to add more energy capacity. Current lithium-ion batteries have electrodes in the form of a positive cathode and a negative anode, and electrolytes in between so charged lithium ions can move around. When charging a battery, lithium ions move from a cathode to an anode for storage. In discharge, the lithium ions move from the anode to the cathode, and out to the device.

The new CFx battery design has a multipurpose electrolyte of solid lithium thiophosphate that can be an ion conductor and also serve as a cathode. The electrolyte can carry charge and hold ions, which helps boost the energy capacity of the battery. The prototype CFx battery has a solid electrolyte, while conventional batteries have liquid electrolytes, Liang said.

"You have an electrolyte that not only does its own job, it provides the function of the cathode," Liang said. "You can also store energy in the electrolyte."

The dual-functioning electrolyte could lead to new battery designs, and new batteries could be in the market in a few years, Liang said. He wasn't able to determine the cost of making such batteries.

"I have no idea of mass production and how much it's going to cost for each individual battery. All the material we use here is abundant.," Liang said.

ORNL researchers worked for three to four years on this battery technology and are researching new solid electrolyte materials, Liang said.

ORNL, based in Oak Ridge, Tennessee, is managed by University of Tennessee, Battelle.

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